The present disclosure relates to a differential transformer magnetic permeability sensor.
A magnetic permeability sensor with the use of a differential transformer (hereinafter, referred to as “differential transformer magnetic permeability sensor”) is known. The differential transformer magnetic permeability sensor is for example used for sensing the remaining toner amount or the toner concentration in an image forming apparatus in which a magnetic toner is used as a developer. Hereinafter, the differential transformer magnetic permeability sensor that senses the remaining toner amount or the toner concentration will be referred to as “toner sensor”.
For example, a toner sensor that senses the toner concentration in a two-component developer includes a multi-layer substrate and planer coils. In the multi-layer substrate of the toner sensor, a first coil is disposed in a first layer, a second coil is disposed in a second layer, a third coil is disposed in a third layer, and a fourth coil is disposed in a fourth layer. For example, the first and fourth coils serve as drive coils, the second coil serves as a reference coil, and the third coil serves as a sensing coil in the toner sensor. The coils are planer coils. The above-described configuration allows the toner sensor to be compact, thin, and light-weight.
The sensor can be attached to a side of a developing device for a magnetic one-component developer. In this case, the output of the sensor changes according to the level (amount) of the magnetic toner in the developer. Thus, the sensor can be used for sensing the remaining toner amount.